Interaction between biomembrane models based on Langmuir films and giant unilamellar vesicles (GUVs) with triazine herbicides and detection via SERS spectroscopy

Author(s)

Rafael Jesus Gonçalves Rubira

• Document type: Doctoral Thesis
• Press: Presidente Prudente. 2020-12-23.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências e Tecnologia. Presidente Prudente
• Defense date: 2020-12-03
• Advisor: Carlos José Leopoldo Constantino

Abstract

This thesis is divided in two aspects, the interaction between herbicides and simple model of the plasma membrane (biological aspect) and the detection of these herbicides (environmental aspect). The biological aspect of the work contains the results of two mimetic systems of the lipid structure of the plasma membrane: Langmuir films (DPPC monolayers) and giant unilamellar vesicles (GUVs - DPPC bilayers). The effects caused by the herbicides ametryn (AMT), atrazine (ATZ) and prometryn (PRM) on phospholipid dipalmitoyl phosphatidylcholine (DPPC) for both mimetic systems were studied. The interactions between phospholipid and herbicides were analyzed by means of DPPC Langmuir films with the herbicides in the aqueous subphase characterized by surface pressure isotherms vs average molecular area (π-A isotherms), Brewster angle microscopy (BAM) and Infrared reflection absorption spectroscopy with polarization modulation (PM-IRRAS). DPPC GUVs were produced using the electroforming technique and characterized by phase contrast microscopy. Both simple models of mimicry showed that the herbicides AMT, ATZ and PRM have some effect on the structuring of DPPC. However, in both systems, AMT was the herbicide that induced the most dramatic changes in this structure: 85% of the GUVs lost their phase contrast (these values were 38% and 30% for ATZ and PRM, respectively) and in the aqueous subphase it was the herbicide that most displaced the π-A isotherms of Langmuir film monolayers to greater values of areas (followed by ATZ and PRM) and also the only one to cause rupture in this monolayer. In the environmental aspect, the detection of herbicides (PRM, AMT and ATZ) was carried out using the surface-enhanced Raman scattering (SERS). As SERS platform, silver nanoparticles (AgNP) were used, characterized by UV-Vis absorption spectroscopy, dynamic light scattering (DLS) and zeta potential. Herbicides suffer hydroxylation in acidic environments and this directly interferes in the affinity with the surface of AgNP, crucial in SERS. At pH < 5, PRM and AMT interact with AgNP through C = O, while at pH > 5 the interaction occurs in the protonated nitrogen. It was not possible to obtain SERS spectra from ATZ at pH > 2, probably due to the low affinity with the metallic surface, the chlorine (Cl) present in its molecular structure hinders the adsorption on the metal. In the quantitative analysis, the PRM presented adsorption isotherms of the Langmuir type while the AMT showed isotherms of the sigmoidal type. The detection limit (LOD), determined in the linear range of each isotherm, was 9.2 ppb for PRM and 3 ppb for AMT, these concentrations are below the limit allowed by the regulatory agencies for drinking water, in Brazil, and in Europe. (AU)

• FAPESP's process: 16/09634-0 - Interaction between biomembrane models based on Langmuir films and giant unilamellar vesicles (GUVs) with triazine herbicides and detection via SERS spectroscopy.
• Grantee: Rafael Jesus Gonçalves Rubira
• Support Opportunities: Scholarships in Brazil - Doctorate